1. Field of Invention
The invention relates to medical instruments and more particularly to a safety syringe which, after a single use, can be discarded for preventing contamination by retracting the needle into the syringe barrel and breaking the plunger.
2. Description of Related Art
Safety syringes are medical instruments for dispensing liquid preparations or withdrawing liquid medicines. However, medical employees such as doctors and nurses are liable to accidental puncture of the skin by a needle. The problem can be serious if the needle has been used. Recently, diseases (some fatal), such as hepatitis and Acquired Immune Deficiency Syndrome (AIDS), can be contracted if the needle has been used on an infected person. For preventing contamination, safety syringes are developed and commercially available.
A conventional disposable safety syringe comprises a barrel, a plunger inserted into the barrel, a needle hub provided at a front end of the barrel to hold a needle, and a block member having a through hole provided in the needle hub. The barrel has an annular groove on a front wall around the needle hub. After engaging the head of the plunger with the needle hub, the plunger can be pulled backward to break the groove so that the needle hub and the needle are retracted into the barrel.
However, in the conventional safety syringe the thin groove on the front wall of the barrel may be broken during injection or transportation of the safety syringe due to thermal expansion and contraction of PP (polypropylene) material of the safety syringe, thereby causing a leakage of the fluid medicine. Further, the desired retraction of the needle hub into the barrel can be jammed due to temperature variations. Thus, the need for improvement still exists.